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Old 10-08-2009, 01:11 PM   #1 (permalink)
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Smaller radiator for FE?

I was looking through the vehicle mods again and I started thinking: given the way most of us drive, would a smaller radiator help FE? A lower overall volume of water and smaller radiator surface area should improve warm-up times. Additionally, a shorter water path should decrease the back pressure on the water pump, meaning less power is required to pump the same volume of water.

The downside is obvious. We could increase the risk of overheating. So I'm not suggesting cutting the radiator size in half. It is also more likely that your fan will kick on more often.

What are your thoughts?

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Old 10-08-2009, 01:35 PM   #2 (permalink)
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Smallest radiator possible with the highest cooling capacity available.

I think most of the pressure in the system comes from the amount of times the water has to change directions, not necessarily from the radiator. Measure pressure drop across the inlet and outlet of a radiator, at whatever CFM the fluid flows, and then do the same through all the passages of the block/head. I'm sure you'll find that it's much greater in the engine.

I had honestly considered replacing the radiator in my Civic when it started leaking from the end tanks (before I learned how to fix them) with some from a bike, which are much smaller. I never actually did it, but my Civic always ran over-cooled without the thermostat in it, and one of my goals was to be able to remove the t-stat and still have normal warm up times without overheating.
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Old 10-08-2009, 01:46 PM   #3 (permalink)
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Quote:
Originally Posted by Christ View Post
Smallest radiator possible with the highest cooling capacity available.

I think most of the pressure in the system comes from the amount of times the water has to change directions, not necessarily from the radiator. Measure pressure drop across the inlet and outlet of a radiator, at whatever CFM the fluid flows, and then do the same through all the passages of the block/head. I'm sure you'll find that it's much greater in the engine.
I agree - most of the pressure drop occurs in the engine. But replacing a radiator is much cheaper than the engine . But the point is to actually lower my available cooling capacity (water volume and surface area) to improve warm up times and SLIGHTLY reduce back pressure (that piece may only be worth 0.1mpg or less).
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Old 10-08-2009, 01:48 PM   #4 (permalink)
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Quote:
Originally Posted by chuckm View Post
would a smaller radiator help FE?
For the reasons mentioned, I think it would.

Plus a smaller radiator would permit a smaller grille opening, bringing established aero benefits.
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Old 10-08-2009, 01:50 PM   #5 (permalink)
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Quote:
Originally Posted by chuckm View Post
I agree - most of the pressure drop occurs in the engine. But replacing a radiator is much cheaper than the engine . But the point is to actually lower my available cooling capacity (water volume and surface area) to improve warm up times and SLIGHTLY reduce back pressure (that piece may only be worth 0.1mpg or less).
That's why I wanted to get a setup that would still allow proper and full warm up without the t-stat installed.
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Old 10-08-2009, 03:04 PM   #6 (permalink)
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Changing the radiator on a thermostat equipped motor would not decrease warm-up time since that is controlled by the thermostat. The water pump tries to move the same amount of water at a specific RPM no mattter what the size of the radiator and quite possibly a larger radiator would have less flow resistance and reduce the load on the pump. If you want to reduce the load on the pump then look into an underdrive pulley set which would slow both your water pump and alternator and reduce the load of both.

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Old 10-08-2009, 03:51 PM   #7 (permalink)
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Quote:
Originally Posted by micondie View Post
Changing the radiator on a thermostat equipped motor would not decrease warm-up time since that is controlled by the thermostat. The water pump tries to move the same amount of water at a specific RPM no mattter what the size of the radiator and quite possibly a larger radiator would have less flow resistance and reduce the load on the pump. If you want to reduce the load on the pump then look into an underdrive pulley set which would slow both your water pump and alternator and reduce the load of both.
It is possible that a smaller radiator would have more flow resistance if the tube diameter were smaller or there were more turns. However, the pressure drop also varies directly by the length of the water path. A smaller radiator is likely to have the same size tubing, fewer turns, and lower length.
I agree that the volume of water pumped will not change. But the overall volume of water contained in the system will decrease, meaning a smaller heat sink and faster warm up times.
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Old 10-08-2009, 04:08 PM   #8 (permalink)
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People have done "half radiators" and talked about it on GS but I don't recall the details.
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Old 10-08-2009, 04:27 PM   #9 (permalink)
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...well, here's my "DIM LIT LIGHT BULB" idea submission:

...how about selectively dumping the exhaust through a portion of the radiator to speed-up coolant temperature-rise and thus initial engine warm-up.

...maybe a thermostatic "dump" value (like the old exhaust "rattler" used to 'crossover' the exhaust through the bottom of the carburated intake manifolds).

...sends 'some/most' of the exhaust thru the small radiator when COLD, but once reaching operating temp then sends 'all' exhaust through regular exhaust system as normal.
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Old 10-08-2009, 08:03 PM   #10 (permalink)
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Quote:
Originally Posted by micondie View Post
Changing the radiator on a thermostat equipped motor would not decrease warm-up time since that is controlled by the thermostat. The water pump tries to move the same amount of water at a specific RPM no mattter what the size of the radiator and quite possibly a larger radiator would have less flow resistance and reduce the load on the pump. If you want to reduce the load on the pump then look into an underdrive pulley set which would slow both your water pump and alternator and reduce the load of both.

Christ: Why do you run no stat?
That's not true at all. The thermostat doesn't just stay open, this is the reason that grille blocks afford a shorter warm up time. The thermostat opens when the water touching it reaches a specific temperature. As the flow rushes past it, it cools down, lower than the temp at which the t-stat would be open, so it closes again. This heats the water up again inside the block. This happens several times before the engine has actually warmed up. A smaller radiator (or a grille block) prevents the water from cooling as much between cycles, so there are less cycles of heating and cooling until complete warm up.

I don't run with no thermostat. It was a goal I had, to be able to run without one and still have normal warm up times and no overheats. T-stats represent a fairly large restriction to flow, even when open fully, which loads the water pump. It's a negligible amount of power, but it's not like it'd be hard to do, and the smaller radiator has obvious aero benefits as well.

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